This invention relates to a chlorotrifluoroethylene based copolymer which is soluble in various organic solvents, curable at relatively low temperatures and suitable for use as a paint vehicle.
Fluororesins are generally excellent in chemical resistance, weather resistance and heat resistance. Accordingly paints using a fluororesin as the vehicle have been developed for application to, for example, chemical plants, buildings and other constructions, machinery and food containers. Recently much attention has been directed to solvent-thinned paints using a fluororesin which is soluble in organic solvents and curable at relatively low temperatures. Fluororesin paints of this type are comparable to paints using other conventional resins in the ease of application and provide paint films superior in chemical resistance and weather resistance.
To render a fluororesin soluble in practical organic solvents, usually it is necessary to reduce crystallinity of the fluororesin by copolymerization thereby to accomplish internal plasticization. There are some other problems to be resolved for using a soluble fluororesin as a paint vehicle. The problems include how to retain a desirable degree of rigidity or shear modulus in the modified fluororesin, how to control the molecular weight of the fluororesin with a view to desirably adjusting the viscosities of paints and how to select and control the kind and amount of a functional group to be introduced into the fluororesin in order to render the resin curable. The cost of manufacture also has to be taken into consideration. It is not easy to reach a balanced solution for all the problems.
U.S. Pat. No. 4,631,326 discloses a copolymer of, essentially, chlorotrifluoroethylene (CTFE), a fatty acid vinyl or isopropenyl ester and a hydroxyl-containing allyl ether such as ethylene glycol monoally ether. This copolymer is soluble in various organic solvents and curable with a polyisocyanate or a melamine resin, and the cured copolymer is hardly soluble in organic solvents in which the uncured copolymer is soluble. Therefore, a solution of the copolymer is useful as a liquid vehicle of a paint.
The CTFE based copolymer of U.S. Pat. No. 4,631,326 provides paint or coating films which are fairly good in physical and chemical properties. However, in our view it is desirable to further improve that copolymer in respect of water resistance, acid resistance and abrasion resistance without sacrificing other properties including good solubilities in various organic solvents and curability at relatively low temperatures.